By the incineration of waste, a reduction of the amount of waste is obtained, and it is made possible to use the released energy for power and/or heating purposes, but at the same time there is obtained a concentration of environmentally foreign or environmentally noxious constituents, such as heavy metals, in the ash and the other solid particle fractions, and a flue gas which also carries hazardous compounds, both mineral and organic, such as halogen compounds, is also obtained.
The flue gas from the incineration can be cleaned with respect to solid as well as gaseous contaminating constituents by means of various known methods whereby further particle fractions of flue gas cleaning products (FCP) can be produced.
When ash fractions and other by-products from the incineration of waste are used or landfilled, a dissolution and leaching of the environmentally foreign or environmentally noxious compounds can take place resulting in a contamination of the environment.
This effect can be removed or reduced to an acceptable level by extracting the environmentally noxious compounds for reuse or disposal of reduced volumes, or the compounds can be immobilized by coating the particles and/or binding the compounds chemically by means of additives or thermal treatment.
It is known to return boiler ash, filter ash, flue gas cleaning products and grate screenings and to sinter or melt these materials together with the slag, e.g. by introducing them in the rotary kiln inlet in a grate/rotary kiln plant.
Likewise, much experience has been obtained by melting together various of these fractions in order to obtain stabilized materials.
Processes are known for extracting, with e.g. acid containing water, a series of metals from the ash products, which are thereafter made into briquettes for being returned to the incineration plant so that the material can form part of the slag.
It is also known to add cement, silicates, iron oxide or phosphate, whereby the materials are stabilized markedly with respect to the washing-out of heavy metals.
Thus, it is possible to achieve that certain residual products or materials can be used as secondary building materials or be deposited.
For more detailed descriptions of the said methods reference is made to the literature, e.g. the references cited in the following.
However, the ash from waste incineration plants is typically subject to such variations that it has been difficult to provide a safe and economical method for securing the reuse of the ash products.
In the method known from the Danish Patent Application No. 6379/89 there is, in principle, also used ferrous compounds in connection with stabilization. In this method aluminum silicates, lime, ferrous iron and water are mixed to a liquid mass and subsequently dried to a concrete-like solid waste product, but this method does not comprise a washingout step, and ferrous iron is only one of several stabilizing chemicals which lead to the formation of a concrete-like product.
Likewise, it is known from Japanese Patent Application No. J 62183896 that coal ash can be treated with iron containing compounds in order to improve the utility of the ash, but also this method does not comprise a combination with washing-out or subsequent oxidation and, if desired, thermal treatment.
From e.g. EP Patent No. 0 536 268 B1 it is known to introduce ashes and other flue gas cleaning products in the combustion zone of a waste incineration plant for thereby obtaining a melting together with the slag and thereby an immobilization of heavy metals etc. in the slag, but one may hereby obtain an undesired release of noxious constituents to the flue gas, e.g. Pb, Hg, As and Zn.
It is the main object of the invention to provide such a safe and economical method for the stabilization of the residual products from waste incineration that they can be used without risk as filling materials or be landfilled without contamination of the environment.
It is also an object of the invention to provide a plant for carrying out the said method.